On 24 January 2018 at 23:02, Dan Rue dan.rue@linaro.org wrote:

On Mon, Jan 22, 2018 at 07:52:57PM +0530, Naresh Kamboju wrote:

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On 20 January 2018 at 07:52, Linaro QA qa-reports@linaro.org wrote:

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Summary

kernel: 4.15.0-rc8 git repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git git branch: master git commit: 8dd903d2cf7b6dfe98be7c19f891882583c7266e git describe: v4.15-rc8-225-g8dd903d2cf7b Test details: https://qa-reports.linaro.org/lkft/linux-mainline-oe/build/v4.15-rc8-225-g8d...

Regressions (compared to build v4.15-rc8-120-gdda3e15231b3)

x86_64: kselftest: * fsgsbase_64

Re-submitted job

fsgsbase_64 test failed 2 out of 10 times. Need to investigate the real reason for failure.

Fail log:

[RUN] ARCH_SET_GS(0x0) and clear gs, then schedule to 0x1 Before schedule, set selector to 0x1 other thread: ARCH_SET_GS(0x1) -- sel is 0x0 [FAIL] GS/BASE changed from 0x1/0x0 to 0x0/0x0

<trim> [RUN] ARCH_SET_GS(0x1), then schedule to 0x200000000 Before schedule, set selector to 0x2 other thread: ARCH_SET_GS(0x200000000) -- sel is 0x0 [FAIL] GS/BASE changed from 0x2/0x0 to 0x0/0x1

https://lkft.validation.linaro.org/scheduler/job/100583#L2613

• Naresh

I looked into this a bit and I think it's a bad test.

We've seen it fail all the way back in 4.14-rc6 (about as far as our data goes): https://lkft.validation.linaro.org/scheduler/job/20773#results_3354469

The failure rate is much less than 20%. Sometimes when I run it in a loop I can get several hundreds of runs before it fails, but it will always fail eventually, which explains why we see it so infrequently.

The most recent commit to fsgsbase.c says:

commit 23d98c204386a98d9ef9f9e744f41443ece4929f
Author: Andy Lutomirski <luto@kernel.org>
Date:   Tue Aug 1 07:11:36 2017 -0700

    selftests/x86/fsgsbase: Test selectors 1, 2, and 3

    Those are funny cases.  Make sure they work.

    (Something is screwy with signal handling if a selector is 1, 2, or 3.
    Anyone who wants to dive into that rabbit hole is welcome to do so.)

I think we may be seeing the "something screwy".

I vote to file the bug (naresh), report the issue upstream (drue), and then add it to the skiplist.

LKFT: mainline: x86: kselftests fsgsbase_64 failed - GS/BASE changed from 0x1/0x0 to 0x0/0x0 https://bugs.linaro.org/show_bug.cgi?id=3596

- Naresh

Dan